The two amines, octopamine and serotonin, function as neurohormones in lobsters. They are found in association with a group of 100 neurosecretory neurons widley distributed in the thoracic region of the lobster nervous system. Our earlier studies were concerned with the activation and physiological properties of these neurons, the release of the amines and the metabolism and targets of the amines in different parts of the organism. With this proposal we plan to continue our studies with this system. First, we will attempt to find the sensory neurons that activate the neurosecretory cells. Second, studies will examine the pre- and post-synaptic physiological actions of the amines at neuromuscular junctions in detail with a view towards the isolation of the amine-sensitive components. Third, studies, modelled on those already carried out, will examine the role of dopamine and the pericardial peptide in lobsters. Fourth, the actions of serotonin at lobster neuromuscular junctions will be compared with the effects of catecholamines at vertebrate muscle junctions. Fifth, a series of preliminary experiments will attempt to understand how the amine neuron systems affect lobster behavior. Our proposed studies may be of considerable value in understanding the functioning of a neurohormonal system from the level of the natural stimuli that activate the system, through a detailed understanding of how amines work on target tissues, and ultimately, to a knowledge of how amines affect the animals behavior.